1. Technical Field
The present invention relates to a contour correction device.
2. Background Art
A contour correction device is in use for correcting a contour of a video image and preventing blurring of a video image by emphasizing a harmonic component of a video image signal.
As shown in FIG. 7, a contour correction device 100 of related art comprises a high-frequency pass filter (HPF) 10, a multiplier 12, a limiter and coring processor 14, and an adder 16. An input video image signal is input to the HPF 10, only signals of a frequency band of greater than or equal to a predetermined cutoff frequency are extracted, and, after an amount of correction is adjusted by the multiplier 12, the extracted signals are input to the limiter and coring processor 14. As shown in FIG. 8, the limiter process is a process to limit the absolute value of the extracted contour component so that the absolute value does not exceed a predetermined limit value. As shown in FIG. 8, the coring process is a process to inhibit the absolute value of the output signal when the absolute value of the extracted contour component is within a predetermined range. The signal to which these processes are applied is added to the input signal by the adder 16, and the resulting signal is output. In FIG. 8, the input signal to the limiter and coring processor 14 is shown by a broken line and the output signal is shown by a solid line.
With such a process, a high-frequency component of the video image signal is emphasized, the contour of the video image is corrected, and sharpness of the video image is improved.
In the contour correction device of related art, the contour correction process is uniformly applied independent of the video image signal. Because of this, as shown in FIG. 9, an edge (contour) component having a large change is emphasized, but a texture component which is a fine change is not significantly emphasized, and the effect of the contour correction has been insufficient. On the other hand, if the gain is to be increased in order to emphasize the fine texture component, there has been a problem in that the edge (contour) component is emphasized too much.
In addition, when noise is superposed on a flat portion having a small change as a video image, there has been a problem in that the noise component is emphasized when the noise component cannot be removed by the coring process.
Moreover, with the emphasis of the edge portion, there has been a problem that ringing may be caused in which the brightness of a peripheral portion of the edge becomes excessively high, resulting in a white display.